It seems like a great idea, and I wonder why I haven't heard it before. Of course the idea of encountering alien AI in space is nothing new... some scientists even think that somewhere out there there may be aliens who have transformed themselves into intelligent machines. That may sound strange, but with the advent of hearing aids, artificial limbs, pacemakers, and even bionic eyes, futurists have long wondered how far we humans will go in transforming ourselves with technology -- becoming more and more like cyborgs, integrating machinery into our bodies until we are more machine than man, and perhaps one day shedding our biological vehicles altogether, transferring only our consciousness to a super computer. Maybe then we will live in a robot civilization, or perhaps our bodies will be spaceships, and we will travel between the stars for ages, powered by nuclear fusion, or some exceedingly remote technology. These might be our distant relatives, maybe resembling something like the Voyager spacecraft drifting endlessly in the darkness, except that they might still harbor a pioneering spirit carried on from humankind, and some notion of whence they came.

The idea of turning ourselves into machines isn’t exactly heartwarming, but it does have its advantages. Machines could live much longer in space than our fragile bodies. Life support is extraordinarily economical with no food or potables to carry. The vast distances between the stars can be traversed without the human problem of aging, and without the relativistic tragedy of rushing fast into the future and leaving a family behind forever. And of course turning ourselves into spacecraft would mean the capacity to survive a catastrophic event on Earth, like a monstrous cometary collision or the eventual death of our Sun.

Whether we’re looking for extraterrestrials who have become machines, or just the artifacts of extraterrestrials, it really just becomes a question of odds. On the one hand, we’re opening up new avenues of exploration, thinking about ways to find life (or intelligence) as we don’t know it, and that would seem to increase our chances of finding something. But at the same time, we’re diluting the resources. In other words, the more kinds of intelligence signatures we look for, the less time we can devote to each, and since SETI is now funded primarily by private sources, telescope time is at a premium. That’s probably why Shostak is suggesting we look for these other things only a few percent of the time.

But what are we more likely to find, biological life forms, or their technological offshoots? The case for the latter is compelling. Shostak uses the Drake Equation as his jumping-off point, taking for granted an inevitable leap into Artificial Intelligence technology for advanced civilizations. If these smart machines are able to outlast their inventors, he argues, then statistically it's more likely that we will encounter them. But even neglecting these calculations, it is a good bet that we might encounter some kind of artificial, space-faring sign of intelligence. For reasons mentioned above, it makes a lot of sense to send robotic emissaries into space on behalf of a biological species. We’ve been doing it for years: for relatively little cost, we’ve sent robots to do our bidding across the solar system, and their recon work is superb. They can spend years speeding through the dark, a job which, until we master hibernation, would be maddening for humans. And we don’t feel too bad about not giving them enough propellant to return to Earth. We’ve now got four spacecraft (five if you include New Horizons) on their way out of the Solar System, and it’s likely there will be more to come. A civilization far more advanced than ours could have robotic spacecraft flocking through the galaxy, perhaps equipped with their own radio telescopes, plumbing the depths of space in search of other voices. Such an advanced civilization could extend its reaches far beyond its home world, creating an outsized presence that could be easier to detect.

We should be careful not to get ahead of ourselves, though. There is already a high bar set for interstellar communication: the civilization has to have radio astronomy. This is no little problem, because we’ve only had it for about 75 years or so. But there was no shortage of interesting people to talk to here on Earth before the 1930s. Modern civilization stretches back thousands of years, and complex life is billions of years old! But until the 20th century, from a cosmic perspective we were a silent world. Obviously, a silent world is not necessarily an uninhabited world. An alien civilization (depending on their experience, I guess) would probably have been just thrilled to find the trilobites scurrying around on our planet 400 million years ago, or the dinosaurs stomping about 70 million years ago; but such a discovery would almost certainly have been an accident. Our astronomers would be ecstatic to find even a fossilized microorganism on Mars, so you can imagine what the discovery of any living, complex organism would be like. The capacity for interstellar communication is not a requisite for being an interesting planet, or species. But if there are dinosaur analogs on a planet orbiting a star just a few light-years away, there’s no way for us to hear from them. There may be many such worlds nearby, teeming with living wonders but utterly cut off from the universe. Short of an expedition, or definitive evidence from a spectroscopic analysis of the planet, we will have no clue as to what resides there.

As soon as we start raising the bar for the technology of extraterrestrials, we run the risk of missing other civilizations that might not be quite as advanced. It’s exciting to think about alien machines huddled around hot young stars and harvesting that massive energy for their futuristic business, but for the moment, looking for life the old fashion way might still be best. And even if there are robots operating with technology thousands or millions of years ahead of ours, I suspect they'll still be able to recognize our signals. Hopefully, we'll be able to recognize theirs.